The proposed research focuses on the C. parvum P-glycoprotein homologue (Pgh), Pgh is a member of the ABC class of transporters. Pgh is an important target to study in C. parvum as it is known to be refractory to most drugs tested to date. It is not known whether drug transport is the major contributory factor or actual resistance to all the many drugs tested to date. The specific aims of this research are (1) complete the cloning and sequencing of the C. parvum pgh gene; (2) obtain expression of the Pgh transporter in Saccharomyces cerevisiae in such a way that a functional assay can be developed; and (3) use the yeast system as a functional assay of Pgh to test inhibitor activity.